I am curious to know what are the problem of homebrew itself ?
As a generic user who has never done anything really complex with it, homebrew is a joy, it has never failed me.
Typically the problem areas would be in versioning of dependencies (in particular, resolving conflicting version requirements for different packages, where dependencies form a DAG rather than a tree) or around install hooks (where installation / removal can't be represented simply by existence / absence of whole files on the filesystem).
Nix is reproducible, supports easy rollbacks, and can manage multiple versions of everything for different projects. You don't have to worry about "works on my machine" or "don't update X right now because Y will break" when collaborating.